Thermal switch



May 28, 1968 J, ROPER 3,385,940

THERMAL SWITCH Filed Oct. 21, 1966 IN V EN TOR.

BY mm mm United States Patent 3,385,940 THERMAL SWITCH John Roper, 1325 Eutaw Place, Baltimore, Md. 21217 Filed Oct. 21, 1966, Ser. No. 588,453 2 Claims. (Cl. 337-403) ABSTRACT OF THE DISCLQSURE A thermal switch for preventing damage to a combustion engine in the event of overheating due to the loss of engine coolant having an element, fusible at relatively low temperature, immersed in the engine coolant and electrically in circuit with a component of the engine necessary to its operation and resilient means operable upon the fusible element to collapse the same and break the electrical circuit therethrough and thus stop the engine when the engine overheats and the element fuses.

This disclosure relates to a device that prevents internal combustion engines from committing self-destruction from over-heating.

It is an object of this invention to provide a simple, foolproof and reliable device which will prevent damaging elfects to an internal combustion engine due to overheating such as may occur when liquid coolant for the engine is lost due to leakage or boiling away.

In general, the system is dependent on an alloy that melts at 240 F. The failure of the alloy to withstand temperatures above 240 F. insures protection to the engine from over-heating. When the alloy melts, the engine stops. A well known alloy which melts at approximately 240 F. consists of 53.7% bismuth and 46.3% lead.

In detail, the alloy is a link in the electric circuit that supplies current to an engine component necesary to its operation as, for example, the engine fuel supply. When the alloy melts, the link is broken and the fuel is cut off.

In more detail, a standard pipe plug is modified to contain the elements necessary for this unit.

Referring to the drawings:

FIGURE 1 is a sectional view of the device installed in the wall of the water jacket of an engine cylinder head; and

FIGURE 2 is a fragmentary view of the device showing the same after it has been subjected to excessive heat.

Bolt or stem 2 is under tension from nut 5. The low melting alloy 3 is held in contact between the bolt head 2, metal washer and the plug face 4. The fiber washer 6 is electrical insulation. Plastic tube 7 is an electric insulator. Electric connection 9 is the ground leg of the circuit of the engine component such as the fuel circuit not shown in detail.

During normal operation, the fuse metal 3 is covered by the liquid in the cooling system and is at a temperature of say 180 F. If and when the fuse metal 3 is uncovered due to the loss of the cooling liquid while the engine is in operation, the cylinder head 1 undergoes a rapid rise in temperature. Should the engine be allowed 3,385,940 Patented May 28, 1968 to continue operation, the heat rise will destroy the engine. The cylinder head 1 is most sensitive to the cornbustion process, therefore, the first abnormal heat in cylinder head 1 is conducted to plug face 4, then passed on to washer 10 and finally when alloy 3 reaches 240 F. the face of alloy 3 against washer 10 softens. The washer 10 is under pressure from the elastic in compression in cavity 8. This compression force on washer 10 is relieved by the heat softening alloy 3. This relief is expressed in a movement or travel of washer 10 from the plug face 4. This motion makes an air-gap 11 between plug face 4 and washer 10 as shown in FIG. 2. This air gap 11 disconnects electric circuit 9, stopping the engine before damage or destruction from further over-heating.

What is claimed is:

1. A thermal switch comprising:

(a) a plug having a bore therethrough adapted to be installed in an opening in an engine cooling jacket with the inner end thereof exposed to the engine coolant;

(b) a stem member extending through the bore in the plug and having a head at its inner end and an electrical terminal means at its outer end;

(0) a sleeve of electrical insulating material surrounding the stem in the bore;

(d) a member of low melting point metal alloy surrounding the stem and contacting the head;

(e) a metallic washer surrounding the stem between and in pressure contact the metal alloy member and the end of the plug, and

(f) a resilient means at the end of the sleeve and exerting pressure against the washer whereby upon melting of the alloy member due to overheating thereof the resilient means will move the metallic washer out of contact with the end of the plug and break the electrical circuit from the terminal at the outer end of the stem through the stem, alloy member and washer to the plug.

2. The structure defined in claim 1 in which the outer end of the stem is provided with a screw thread, and a nut is threaded on the threaded stern, and a washer of insulating material is positioned between the nut and outer end of the plug, and in which the electrical terminal is clamped between said nut and a second nut threaded to said stem.

References Cited UNITED STATES PATENTS 9/1925 Colby 200142 XR 10/1927 Pletscher 200142 FOREIGN PATENTS 1912 Great Britain. 3/ 1933 Germany. 5/ 1956 France.

WENDELL E. BURNS, Primary Examiner.

Huntley 200142 

